Optimizing Cu 3d Bands with Nanotubular SnO2 to Boost Their Catalytic Transfer Hydrogenation Activity.

Catalytic transfer hydrogenation (CTH) using Cu nanocatalysts offers significant advantages over direct high-pressure hydrogenation. However, the active hydrogen (H*) in this process exhibits poor adsorption and tends to release H₂ readily due to the fully occupied 3d states of Cu. To address this issue, a tubular SnO₂ support with electron-accepting ability was selected to host Cu nanoparticles, aiming to optimize the Cu 3d bands. The Cu/SnO₂ nanohybrids were prepared through an electrospinning technique, followed by hydrothermal synthesis. As evidenced by X-ray photoelectron spectroscopy (XPS) binding energy shifts and density functional theory (DFT) simulations, some electrons from Cu transferred to SnO₂ in the Cu/SnO₂ nanohybrids due to their different work functions. Such electron transfer enables the Cu 3d orbitals to lose electrons and alters its valence configuration from 3d¹⁰ to 3d^10-x, which enhances the adsorption of active H* atoms and thereby inhibits undesirable H₂ release. The 15 wt % Cu/SnO₂ exhibits improved catalytic hydrogenation of 4-nitrophenol with NaBH₄, with an optimal normalized rate constant of 56.98 mg^-1 min^-1 and a turnover frequency of 4.82 min^-1, surpassing most reported catalysts. The enhanced activity is attributed to the optimized electronic states, improved hydrogen adsorption, and the tubular structure of the support. This work might shed light on developing more non-noble metal nanocatalysts for CTH by tuning their d bands with appropriate oxide supports.